Transceivers are widely used in the field of mobile communications, for example GSM, UMTS and Long-Term Evolution, LTE. For example, during the installation of a transceiver of a communication system, it can be desirable to perform various tests with the transceiver, preferably without the influence of an antenna-air interface. To this end, some transceivers are provided with a loopback feature which makes it possible to take an output of a transmit (TX) path of the transceiver as an input of the receive (RX) path of the transceiver. In this case, TX path and RX path are set to work with the same radio frequency.
Such a loopback feature may be implemented inside an antenna duplexer connected to Transceiver TX output and Transceiver RX input. However, a loopback in the antenna duplexer increases the complexity and the costs of the duplexer.
Another possibility for loopback is to implement a connection using directional couplers at the output of the TX path and at the input of the RX path and to form a connection by means of a strip line integrated on a printed circuit board. However, if the strip line is integrated on the same circuit board as the transceiver, the strip line crosses the circuit board from a TX side to an RX side of the transceiver. As the length of the strip line is not negligible and an insertion loss increases for increasing frequencies, the loopback driver amplifier gain may need to be increased and coupling factors of the directional couplers may have to be set accordingly. Furthermore, other signals on the circuit board may couple with the strip line of the loopback.